1. Field of the Invention
The present invention relates to the field of bone fixation wherein two or more bone parts, for example pieces of a broken bone, must be kept together to be firmly welded, for example, and more particularly the invention relates to an assembly formed by at least one plate and a screw, the assembly being of the type wherein the plate is provided with at least one orifice transversally passing through the plate with the orifice receiving the screw and the screw being provided with an upper head that is housed into a cavity defined into the orifice.
2. Description of the Prior Art
It is well known that in treatments of degenerative spine disc pathologies, traumas and tumors, for example, plates for promoting the bone welding are used, wherein the plates are placed and fixed to the bone pieces in order to firmly and rigidly keep the pieces in position relative to each other, the plates being fixed to the bone pieces by screws that are passed through orifices in the plates and screwed into the bone pieces.
Once the plate has been placed and fixed to the bones and the wounds resulting from the surgical operation have been closed, the patient lives the hospital and the normal movements of the patient may cause small relative movements of the bone pieces under fixation which causes the screws to be moved and get loose enough to be released from the corresponding orifice of the plate. Under these circumstances the patient undergoes a potential risk that the head of the screw moves out of the orifice and enters into contact with tissues and sensitive parts of the patient's body.
Among the several solutions provided to overcome this problem it may be found a technique of deforming or distorting the head of the screw with the purpose of creating points or areas providing a high friction contact between the screw head and the orifice in the plate. This distortion is performing once the screw has been screwed into the patient's bone and is obtained by hammering the screw head with the help of a tool set, such as a hammer and a punch or a stamp. Intensive care must be taken, however, to avoid any risk for the patient that would affect any closer sensitive organ, spinal cord, marrow, etc. In addition, the firm and safe fixation of the screw within the orifice is not guaranteed as long as the distortions are not seriously programmed but they are aleatory.
In other situations the plate is provided with an extra small orifice adjacent to the orifice for the fixation screw, the small orifice receiving an additional small extra screw. Once the fixation screw has been screwed into the bone the extra small screw is inserted and screwed into the orifice of the plate with the purpose that a head of the extra screw enters into forced contact with the head of fixation screw in order to create a mutual interference to avoid the loosening of the fixation screw. It is obvious that this attempt not only does not guarantee a solution as long as the extra screw is also subject to the risk of getting loose from the associated orifice but also this screw creates an additional risk to the patient because this extra screw will be subject to any movement of the fixation screw, that is, the extra screw would be released from the plate in a period of time shorter than the period of time the fixation screw would get loose.
Another attempt to firmly retain the fixation screw in place it has been to provide a small disc covering at least part of the fixation screw once it is placed and screwed in position, the disc being installed and fixed on the plate by a central small screw passing through the disc and screwed into the plate. Again, a new screw, that is a new problem, is provided with the risk being increased for the patient. In this situation, if the small screw of the disc gets loose, not only the small screw will affect the patient but also the disc that gets free within the patient's body.
Another device developed by the patentee of this application is revealed in U.S. patent application Ser. No. 09/154997 for a "BONE FIXATION DEVICE" consisting of a disc-like piece that is riveted to the fixation plate thus avoiding the use of screws and loose parts, the disc-like piece having radial projections and being capable of rotate against a strong friction resistance created between the piece and the fixation plate to avoid any undesired rotation and movement of the disc piece. The disc-like piece is rotatably riveted to the plate, close to the orifice or orifices receiving the fixation screw or screws, and the disk-like piece can be manually rotated so as to place the radial projections over the heads of the fixation screws once they are placed and screwed in the corresponding orifices of the plate. Thus, the heads of the fixation screws remain covered by the corresponding radial projection and prevented from moving out of the corresponding orifice even when getting loose under the effects of the movements of the patient.
As it is apparent from the above description all the solutions appeal to the provision of additional outer elements like screws and discs or plates fixed to the fixation plate with the purpose of forming an interference or blocking to the head of the fixation screw after the fixation screw has been screwed into the bone pieces, with all these additional elements representing not only an additional task for the surgeon but also a risk for the patient by projecting out of the plate and causing a trauma to the patient.
It well known to any person skilled in the art that in a surgery room any additional element or tool results in the need of additional personnel and time for manipulating the elements and to carry out the complex and time consuming task derived from the additional procedures.
It would be therefore convenient to have a new bone fixation assembly that does not need of additional elements that must be handled out of the conventional and necessary fixation plate and screws, wherein the assembly is formed by the essential two basic elements and guarantee a firm an safe permanent retention of the screw into the bone and the plate.
3. Summary of the Invention
It is therefore one object of the present invention to provide a bone fixation assembly comprised of the two essential basic components, namely the fixation plate and the fixation screw, without additional outer elements being provided to be manipulated by the surgery room personnel but the firm and safe retention being guaranteed by retention means safely forming part of the screw.
It is a further object of the invention to provide a plate and screw assembly for fixing bones wherein the plate is provided with at least one orifice having a cavity an the screw is provided with self retaining means that forms part of the screw and provides the necessary resistant force to retain the head against any axial movement once the head of the screw is housed inside the cavity, whereby the head can pivotally move but is prevented from moving out of the cavity, even if the screw has been released from the bone.
It is another object of the present invention to provide plate and screw assembly for fixing bone pieces, the assembly including a plate and at least one screw, the plate including at least one orifice that defines a cavity for housing a head of the screw and the screw head is provided with a resilient retainer for retaining the head of the screw within the cavity with free pivotal movement but prevented from any axial movement, so that the screw is prevented from moving out of the orifice of the plate.
It is still another object of the present invention to provide a plate and screw assembly for use in bone fixation, applied in procedures of joining bone pieces for the welding of the pieces, the assembly being of the type including a plate and at least one screw, the plate including at least one orifice passing through the plate, the orifice defining a housing cavity for housing a head of the screw passing through the orifice, the screw being passed through the orifice and screwed into one of the bone pieces to firmly retain the plate against the bone pieces to be joined together, wherein the head of the screw has resilient means capable of being retained, together with the screw head, inside the housing cavity against any axial movement, whereby the head of the screw being prevented from axially moving back out of the cavity.
It is a further object of the present invention to provide a plate and screw assembly for use in bone fixation, applied in procedures of joining bone pieces for the welding of the pieces, the assembly being of the type including a plate and at least one screw, the plate including at least one orifice passing through the plate, the orifice defining a housing cavity for housing a head of the screw passing through the orifice, the screw being passed through the orifice and screwed into one of the bone pieces to firmly retain the plate against the bone pieces to be joined together, wherein the housing cavity has an upper opening and a lower opening, an intermediate portion being defined inside the cavity between the openings, the intermediate portion having a diameter larger than any diameter of the upper and lower openings, the screw defining a longitudinal axis and the screw head including a resilient cap retained in the head against any axial movement and capable of radially normally yielding relative to the screw axis to enter into the cavity and radially normally expanding back relative to the screw axis to be retained into the cavity together with the head of the screw once inside the cavity, whereby the head of the screw, and hence the screw, being prevented from axially moving back out of the cavity.
The above and other objects, features and advantages of this invention will be better understood when taken in connection with the accompanying drawings and description.